Muscles in health and disease Flashcards
What % of body mass are muscles
40
Apart from movement, what function do muscles have
Store of intracellular ions like potassium
Important for heat production
What happens if there is damage to a single motor neurone
Affects all muscle fibres innervated by that neuron
80-90% of mass will be lost within the month
Remaining motor neurones will sprout and synapse with denervated fibres
What determines the fibre type when re-innervation is occuring
Primary motor neurone
What happens when remaining motor axons sprout to innervate denervated fibres
The motor units enlarge and fibres become grouped
In terms of muscles, why may a baby suffer from infantile hypotonia
Fibres and small and round wtih a few massivelly hypertrophic fibres
Describe the underlying pathophysiology of infantile myopathic hypotonia
- Disproportion between the 2 muscle fibres types
- Type 1 fibres which are usually the large type appear small
- Type 2 fibres which are usually smaller are normal to larger in diameter
What respiration do the 2 types of muscle fibres undergo
Type 1= aerobic
Type 2= both
Which fibre type stains darker and why
Type 2
ATPase demarks fibres with lots of ATPase, and as anaerobic resp less ATPase
How may muscle disorders be diagnosed
Biopsy
EMG
Name 2 inflammatory myopathies
Polymyositis
Dermatomyositis
What is dermatomyositis
An autoimmune disorder associated with microbial infection resulting in proximal muscle weakness
What biochemistry results may be seen in dermatomyositis
Elevated serum creatine kinase
What would an EMG of somebody with dermatomyositis show
Irritability
What would a biopsy of somebody with dermatomyositis show
Variation in fibre size
Central nuclei
Necrosis and regeneration
Infilitrate of inflammatory cells
What lymphocytes invade in dermatomyositis
CD8 positive cells
What inflammatory cells are seen in dermatomyositis
CD8 positive cells
macrophages to remove necrotic fibres
What is the most obvious physical sign of dermatomyositis
Rash– purple and streaky
Heliotrope rash over eye with oedema
What is subcutaneous calcification
Autoimmune connective tissue disease resulting in calcification of muscles and skin
How may subcutaneous calcification be treated (3)
- Corticosteroids
- Azathioprine
- Methotrexate
Describe the course of corticosteroids prescribed for subcutaneous calcification
- High dose 1mg/kg day
- Maintained until creatine kinase normal
What is the 5 and 8 year survival of subcutaneous calcification
5 year= 80%
8 year= 73%
What causes death in subcutaneous calcification
Malignancy, infection, pulmonary involvement
What are the signs and symptoms of inclusion body myositis
Muscle weakness, specifically in finger and wrist flexors, shoulder abductors and knee extensors
Associated polyneuropathy, dysphagia and loss of quadriceps reflex
What is the most common muscle disease of the elderly
Inclusion body myositis
How do fibres appear in inclusion body myositis
Empty vacuoles and clumps of cellular material containing amyloid like material
What structures are found in the filamentous inclusion in inclusion body myositis
Beta amyloid Hyperphosphorylated tau Apolipoprotein E Presenilin 1 Prion protein
What are muscular dystrophies
Progressive genetically linked degenerative myopathies
Name some x-linked muscular dystrophies
- Duchenne and Becker muscular dystrophies
- Limb girdle muscular dystrophy
- Emery- Dreifuss muscular dystrophie
Name some autosomal recessive muscular dystrophies
Limb girdle muscular dystrophy
Emery-Dreifuss muscular dystrophy
Describe what Duchenne MD is
Proximal muscle weakness in first 2 years of life followed by a continuous show decline
Unable to walk by 7-12, death mid 20s-early 30s
How many babies are born with Duchenne MD
20-30: 100,000 males
What are the creatine kinase levels like in babies with Duchenne MD
Elevated
What would a muscle biopsy of somebody with duchenne MD show
Fibre size variability
Endomysial fibrosis
Degenerating muscle fibres undergoing myophagocytosis
What happens in the late stages of duchenne MD
Loss of muscle replaced by fibrotic material and fat
What myopathies can be induced by steroids
Type 2 fibre atrophy
What myopathy can be induced by statins, and in what % of patients
Rhabdomyolysis
What are the features of fibromyalgia
- Widespread muscle pain with associated fatigue and sleep disturbance
- Both sides of the body in axial skeleton
50% of fibromyalgia patients are positive for what
Antipolymer antibodies
What is the normal age and sex of fibromyalgia patient
30-60 Majority female (80-90%)
How is fibromyalgia treated
Tricyclic antidepressant (amitriptyline)
SSRI (fluoxetine)
Exercise
